Some things to work on:
1) Take a big breath and brace before each rep (think ribs down/back flat).
2) Descend a bit slower into the bottom.
3) Push your knees out harder so they stay in line with your toes
4) Cut your depth in the bottom a bit so you stop just below parallel.
5) Stay in your hips on the way up (your are pulling up with your chest a bit as you rise).